1. Field of the Invention
The present invention relates to a gas burning instrument and more particularly to a gas burning apparatus providing a burning control section suitable for various kinds of gases and a safe burning and preventing a set burning amount from being varied irrespective of the fluctuation in the pressure of supplied gas. To this end, the pressure of gas will be jetted from a nozzle is measured to control it in conformity to a desired burning amount. The present invention also relates to a gas burning apparatus capable of easily deciding the failure of a sensor adapted for detecting the temperature of a pan bottom.
2. Description of the Related Arts
FIGS. 25 through 27 show an example of a conventional gas burning apparatus applied to a gas cooking apparatus. FIG. 25 is a perspective view showing the conventional gas cooking apparatus. FIG. 26 is an enlarged view showing an operation panel. FIG. 27 is a schematic view showing the construction of an oven. As shown in FIG. 25, the gas cooking apparatus comprises a burner 1, a temperature sensor 2, a pan holder 3, an ignition/extinction button 4, a thermal power adjusting lever 5, a grill portion 6, and an operation panel 7. The operation panel 7 as shown in FIG. 26 comprises a display tube 8 for displaying a time/temperature, an LED 9 for displaying various kinds of cooking modes, and a key 10 for setting various kinds of cooking modes. For example, in setting a mode for frying fish, vegetable or the like, an operator presses the key 10 and sets a desired temperature by operating an UP key or a DOWN key 11 while the operator is watching a numerical value displayed by the display tube 8. FIG. 27 is a schematic view showing the construction of the oven. An ignition switch 18 is turned on when the ignition/extinction button 4 is depressed, and electric current is supplied to a main electromagnetic valve 12 and a temperature adjusting valve 14 via a control substrate 19. Gas is fed to the burner 1 via the main electromagnetic valve 12, a hand valve 13, the temperature adjusting valve 14, a bypass key 15, a thermal power adjusting needle 16, and a main nozzle 17, with the maximum flow rate of gas regulated. At the same time, an igniter 20 is turned on via the control substrate 19 and an ignition plug 21 is discharged. Then, the burner 1 starts burning and a thermocouple 22 receives heat from the burner 1 and transmits thermoelectromotive force to the control substrate 19. In this manner, burning continues.
The thermal power adjusting lever 5 is operated to move the thermal power adjusting needle 16 in adjusting thermal power. In this manner, combustion amount is adjusted. Otherwise, the power supply of the temperature adjusting valve 14 is turned on and off in automatically adjusting temperature so as to regulate the combustion amount by the bypass key 15 or by the main nozzle 17.
In changing the kind of gas due to removal or the like, it is necessary to exchange or adjust parts such as the bypass key 15, the thermal power adjusting needle 16, the main nozzle 17, a governor for grill, and a damper 23 for taking in primary air.
The conventional thermal power adjusting method has the following disadvantages: 10 Thermal power is adjusted by the thermal power adjusting needle 16 or switched from a strong degree to a weak degree or vice versa by an electromagnetic valve. The burning amount is not measured or controlled. When the pressure of supplied gas fluctuates, it is impossible to adjust the burning amount to a constant value. Accordingly, the allowable range of the pressure of the supplied gas is wide. For example, in the case of 13A gas, minimum gas pressure is 100 mm H.sub.2 O; central gas pressure is 200 mm H.sub.2 O; and maximum gas pressure is 250 mm H.sub.2 O. Even though thermal power is reduced to 100 mm H.sub.2 O, it is necessary for the thermocouple to secure an appropriate thermoelectromotive force to prevent an accidental fire. As a result, the gas burning apparatus is incapable of reducing thermal power to 40% of safety factor. A rapid change occurs in the strength of flame because gas is burnt strongly and weakly by a temperature adjusting valve in adjusting temperature automatically, which gives a user discomfort. In addition, in controlling thermal power by a strong thermal power or a weak thermal power or by the burning period of time, the operation sounds of valves are frequently generated, which is offensive to the ear.
If a pressure sensor fails and as a result, gas leakage occurs because means for preventing the gas cooking apparatus from being fired has not been devised.
Thermal power cannot be reduced to a small thermal power if foreign matter has stuck to a gap of the mechanism of the flow rate control means.
A function of detecting an abnormal pressure of supplied gas is not provided. The abnormal pressure is generated because gas is not supplied sufficiently if an LPG bomb is vacant, a rubber pipe is bent or a cock is half-opened. Therefore, for example, when two ovens are used, the thermal power is weak or gas is ignited but extinguishes soon. A user cannot find the reason easily and hence, telephone calls for repair.
In adjusting gas pressure while it is being detected by a gas pressure sensor, it is necessary that thermal power adjusting period of time is set to be short to prevent boil-over by performing a rough pressure adjustment and a fine pressure adjustment in consideration of the correlation between the pressure-adjusting accuracy of a reducing mechanism, the performance thereof, and the capability of detecting gas pressure.
The pressures of supplied gases are different from each other in conventional gas burning apparatuses. Depending on the kind of gas, the maximum pressure is higher by 40% than the standard pressure. As a result, the temperature of the gas cooking apparatus greatly increases or an abnormal burning occurs due to an abnormal gas pressure.
A conventional two-oven burning apparatus has a small burner having a combustion amount of approximately 2000 Kcal/h and a large burner having a combustion amount of approximately 4000 Kcal/h. The minimum combustion amount of each burner is approximately 400 Kcal/h and 500 Kcal/h, respectively. When the burning amount of gas is reduced further, flame is not formed and extinguishes. Therefore, large and small needles for adjusting thermal power are used for each burner. Consequently, in changing the kind of gas, parts exchanges are required by disassembling a gas cock. In this case, a gas leakage or an erroneous parts exchange may occur.
The minimum combustion amount is not constant because burning speeds and caloric values are different from each other, respectively depending on the kind of gas. Accordingly, it is necessary to provide a needle for setting a minimum burning amount for each kind of gas burner. Thus, a large number of parts and assembling parts are required to use a different kind of gas. Hence, it is necessary to disassemble a gas mechanical block in using a different kind of gas, which requires a skilled work and much time. Accordingly, cost for using a different kind of gas is high.
In using the apparatus as an industrial measuring instrument to measure combustion amount by the pressure sensor, which has not been conventionally adopted, a zero point adjustment can be accomplished in the beginning of use. But in the case of a gas oven, it is difficult for old people or children to perform a zero point adjustment and in addition, an incomplete combustion occurs.
It occurs that the function of the pressure sensor deteriorates with the elapse of time and hence the apparatus cannot be used, which gives a user inconvenience.
If the performance of the apparatus deteriorates with the elapse of time, thermal power cannot be adjusted and a user has an inconvenience in using it.
It is preferable to install a safety device on each burner to cut off gas in consideration of the situation in which one of burning apparatuses provided under each burner fails. But electric power is required in proportion to the number of burners and the manufacturing cost is high.
When the thermal powers of a plurality of burners are simultaneously adjusted by using the pressure sensor, the thermal powers thereof cannot be simultaneously adjusted due to the relationship between the processing speed of the microcomputer and the flow rate control means. It takes much time to adjust thermal power individually. For example, if thermal power is required to be reduced with food contained in a pan placed on one oven being boiled, water in the pan boils over.
In checking the performance of the pressure sensor provided in a gas burning apparatus, a specific checking tool is required in manufacturing the gas burning apparatus. It takes time and labor to install the checking tool on the apparatus and remove it therefrom. A service man does not carry it with him. Therefore, there is problem with the use of the checking tool.
Since conventional gas burning apparatuses do not comprise the pressure sensor, a needle corresponding to each kind of gas is conventionally used. The gas burning apparatus according to the present invention is provided with a universal flow rate control means capable of adjusting city gas ranging from a low Wobbe index to liquified petroleum gas (LPG).
The area through which gas flows is slight in the construction of the universal flow rate control means adapted for the minimum flow rate adjustment of LPG having the highest calorific value. Therefore, the conventional reducing mechanism does not ensure a reliable control of the flow rate of gas.
If dust sticks to the adjusting mechanism of the universal flow rate control means, a countermeasure for preventing the adjusting mechanism from being destroyed is required in consideration of thermal power cannot be reduced to a predetermined value.
The above-described conventional gas oven is more expensive than other conventional gas ovens because of construction. Therefore, it is necessary to take a measure of using some functions of other gas ovens in common.
It is also necessary to take a measure so that the cut-off means gives rise to a gas leakage due to the common use of some functions of both type.
It is necessary to adjust thermal power at a high speed so that the universal flow rate control means can be easily used and does not give inconvenience to a user.
Few conventional gas burning apparatuses need power supply and therefore, can be used during service interruption. Unless the above-described conventional gas burning apparatus can be used in during service interruption, it does not sell well.
It occurs that a conventional detecting means is incapable of detecting the defect of the temperature sensor depending on the content of defect.